Cathode-ray tube pulse demodulator system



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Aon/575k E. LABIN ETAL CATHODE RAY TUBE PULSE DEMODULATOR SYSTEM FiledNov. 13, 1944 Mr/7:5 oF//AcfML-wr EX 2,438,923 CROSS REFERENCE r www MTM. E

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CATHODE RAY TUBE PULSE DEMODULATOR SYSTEM Filed Nov. 13, 144 ssheets-sheet z /439 46 50 48 4; i z 1H s VV ./121 125 /zzc /131748a H1/a EN@ 1FL l 1 f JI 47 [Y [Y /'52 INVENTORS ATTPNFY April 6, 1948.

CROSS REFERENCE E. LABIN ETAL Filed Nov. 13, 1944 SEARCH ROON CATHODERAY TUBE PULSE DEIIODULATOR SYSTEM 3 Sheets-Sheet 3 65A .aire/ az/972'65 Maf 7 j .9 6.4/'0/ --lfA INVENTORS Rif/547%@ Patented Apr. 6, 1948CATHODE-RAY TUBE PULSE DEMODULA- TOR SYSTEM Emile Labn, New York, andDonald D. Grieg,

Forest Hills, N. Y., assignors to Federal Telephone and RadioCorporation, New York, N. Y., a corporation of Delaware A ApplicationNovember 13, 1944, Serial No. 563,152

(Cl. Z50-27) 15 calms. 1

This invention relates to radio receivers and more particularly to ademodulator for time modulated pulses. l

One of the objects of the invention is to provide an improved-method andmeans for translating time modulation of pulses into amplitude modulatedenergy.

Another object of the invention is to provide a method'and means forcontrolling a beam of energy such as a beam of electrons or anelectromagnetic beam relative to a beam sensitive device for translationof various forms of time modulation of pulses into amplitude modulatedenergy. r

One of the features of the invention is the employment of. a cathode raytube or other electron beam producing apparatus together with means forcontrolling the beam and/or the sensitivity 'of a. beam responsivedevice for translation of the time modulation of the pulses intoamplitude modulated energy. The electron beam is caused to sweep througha normal cycle in synchronism with the average timing of the pulses, aswhen the pulses are free of modulating energy. The beam in its movementis caused to either traverse a. beam sensitive device or to move along apath adjacent thereto. The time modulated pulse energy may be used tocontrol coaction between the beam and the responsive device in any oneof several ways. This coaction between the beam and the responsivedevice causes a flow ofv energy in'a circuit associated with the device,the amplitude of such energy being proportional to the time modulationof the pulses.

One method of controlling the coaction between the beam and theresponsive device is to key the beam on and of! according to the leadingand trailing edges of the pulses. When this method is applied, the beamis normally caused to traverse the responsive device during a given partof its cyclic movement, whereby the keying on and oir of the beam inrelation to such apart, controls the coaction referred to.

Another method of control is to deflect the beam according to the pulseenergy. According to this method the beam movement is adjusted so thatthe beam path is normally adjacent the responsive device, and when thebeam is deflected, it is caused to coincide with the responsive devicefor a. time interval proportional to the degree of time modulation ofthe pulses.

A third method of control is to apply the pulse energy to an element ofthe beam responsive device whereby the beam responsive device is maderesponsive to the beam only when pulse energy is applied to suchelement. In this method of control the beam intensity is maintainedconstant, and its path of movement is caused to co-j incide periodicallywith the responsive device.

The above and other objects and features of the invention will becomemore apparent upon reading the following detailed description withreference to the accompanying drawings in which:

Fig. 1 is a. schematic block and wiring diagram of a receiver accordingto the principles of this invention:

Figs. 2. 3 and 4 are graphical illustrations useful in explaining theinvention;

Figs. 5 and 6 are fragmentary illustrations of variations of the energycollector means shown in Fig. 1; and

Fig. '7 is a schematic block and wiring diagram of a further variationof the invention.

Referring to Fig. 1, there is shown a radio frequency `receiver l withan antenna 2 for receiving pulsed radio frequency energy. the radiofrequency carrier being removed .by the usual detector means thereof.The pulse energy thus detected may be modulated according to any one ofseveral principles of time modulation. For

"example, the successive pulses may be time displaced toward and awayfrom each other according to the push-pull type of time modulation orthe pulses may be modulated in width, either symmetrically or bydisplacements only of one edge thereof, or the successive pulses may betime displaced relative to their unmodulated time positions. These arethe more common types of time modulation but it will be clear as thedescription proceeds that practically any type of time modulation ofpulse energy may be demodulated, that is, translated into amplitudemodulated energy, according to the principles of our invention.

The demodulator part of the system shown in Fig. 1, comprises a cathoderay tube 3 having the usual electron gun equipment 4 for producing abeam of electrons which is controlled by grid 5 and shaped by the usualfocusing means 6. The beam is projected between two pairs of deflectionplates, 1, and 9, Il). 'I'he deflecting voltage applied to the plates l,8 control the normal sweep of the beam on the screen il with respect toa beam responsive device or collector I2 which may be disposed on oneface or the other of the screen Il, depending upon the characteristicsof the screen and the collector. The deilecting voltage applied toplates 1, 8 is produced 3 .by a wave producer I3. The producer I3 may besynchronized with the detected pulses through known synchronizing meansI4. Should the wave energy desired be sinusoidal, producer I3 mightinclude a tunable shock excitable capaci- -tance-inductance circuit, orif the wave desired is o! a saw-tooth character, theproducer mightinclude Va known Vrelaxation oscilla-tor adapted t-o be controlled bythe detected pulses. In either case, the wave generated should haverecurring substantially inclined portionsandhavearperiod comparable inat least a harmonic relation-.to the average timing of the pulses. Eorcontrolling the phase relation ofthe .wavenaphase ad- `luster l5 isincluded se that the sweep cyclefof the beam with respect to thecollector I2 and the' average pulse timing will produce the desiredcurrent condition in the output-circuit ftfoffthe collector I2. Thecurrent flow produced inthe circuit I6 may be applied to a low passfilter I1 Aand thence to a utilization circuit such as phiinesd.

The circuit o1' Fig. 1 -is 4arranged `to provide -a selectionwith'respect -to the 'control ofthe -cathoderayjbeam :byl the detectedpulses from -receiver 'rangement I9 whereby a-movablecontact 2li-con-Ttrnls the application oi the input pulses tcreither thegrid'i or overcircuit :2l-to deectiomplates 9, I0. As shown. the-contact 2D ispositioned to apply the p ulses to the grid 5 whereby the lbeamjls'lkeyed on and oil according to 'the occurrence of the Aleading andtrailing edges of each pulse. The grid 5, lfor this position of themovable-contacts Aof switch 19, lsiprovlded with a'highnegav tive biasbybeing -connected over Vcontact-"22 to 'the negative side -of a sourceofi-potential -HC -whose positive side is connected'to 'the -cathode viaground, whereby the grid is normallysbiased to cut or! in the absence ofpulse energy. The.

bias voltage of the grid is controlledby rcontact '22. iMovablecontact-'23 provides a Yground for the P19594 when the switch'is 'inthe`position illustrated in'lig. 1. 'When the contacts Aor switch 1 3.aremoved to thepositlon opposite that shown, 'the contact 23 is movedfree of ground connection 1l, the contact-22 is 4moved 'to a lowsourceof 'biasing potential LC whose positive side is connectedztoground, and contact is movedto close'connection with line 2| to plate 9.The'low 'bias'lfC provided for the grid '5 in this position ai' switcht9 insures a now ofelectrons'to'iorm a .beam o! constant intensity.Uther biasing circuitsor the circuit of Fig. 1 will be apparent to thoseversed 'in the art and. accordingly the details thereof .are omitted.

'For the purpose of explaining the operation `of the system of'-F ig.`1,whentime modulated pulses are applied to grids. the .graphs of'Fig.' 2are' provided. Graph a'illustrates a train of .pulses 25 which is ltimemodulated according tn jthe pushfpullprinciple. It will be notedalsothatthe pulses 'have a given oiset bias. that is to say. theypulses.in the absence o! modulation. 4will assume a paired ont spacedrelationship. Graph 'li-,illustrates a sinusoidal wave 2B such as maybeproduced at wave producer 'I3 'in accordance with the average ltimingithe detected pulses. Graph c 'representsthe coincident vtiming ,oflthecollector 12 at 't2a,"l2b, etc., with respect to a given portion of thecyclical movement of the wave 26 and also the pulse occurrence .timing-as represented by the 'keying on and .off of the beam .at 2Ba,18a,f30aand ila. Graph d represents .at fthe pulse `energy owingin Athe youtxuit circuit x ,sw y

5 time displacement, pulse 29 is shown displaced to the right about 50%,Pulse 30 is shown to be cen- .tered at .zero modulation and pulse 3| isshown displaced about 50% tothe left. The displace- .ment of pulse 28 isshown to key the beam on loor complete coincidence with the collector I2.

'dihecoincidenceof-the keyed-on beam with the lxxdllector at I 2b isshown to have only about coincidence .with.the.collecto while thecentered vpulse:liliashovvn to provide a 50% coincidence .15;.and- .thepulseglluto provide about 25% coinci- .fdencesvith thecollector I2. Thecurrent flow in circuit I6 being proportional to the number of electronsimpinging upon collector I2 during each keyed-:on part of the beamcycle, produces an out- 20 put pulse. as indicated by pulses 27 for thetime positions of pulses 25.

Assume -now that the switch I9 is shifted to -the right so as toprovidea. low biasy LC on grid 5, to apply pulses from receiver I to denection25 plates'e, -I0 vandto vremove the ground connection ..I. Thisselection -is controlled -by 'af switch ar 2t from line `2I. -InV thiscondition it will be assumed'that-the contact 23 'now applies -a.constant voltage from battery 32 te the Vplate 9 in addition to-theenergy of the pulses from receiver I. This,as indicatedin graph 'a ofFig. 3, causes lthebeam 'to sweep Aadjacent the collector I2, as`indicated at' 33.

"For the purpose orillustrating afurther form 'or time-modulation.the-pulse train 34 of graph e 35 is shown to be modulated in width.. Forexample,

fthe successive pulses 35, 36, 31 and A'38 are pro- -gressively greaterin width. The'wave producer I3 may provide either a. sinusoidal orsaw-tooth `wave-substa-rxtiallyes indicated at 39 and 40 in 40 graphJ'lfor" application to the deflection plates '1 andf. "The-pulse 36represents the pulse width -in--'the'absence of a modulating signal.`When this pulse energy -is applied to the deiiection plates 9 and 10,the beam, which now is keyed on constantly at -a given intensity isdeflected for interception with the collector as indicated at 42h. Theoutput energy of the collector circuit fi :is indicated at 4I, graph h,which vis of ampli- "tude' proportional to Athe electrons collected by.50 the-deflection produced in response to pulse 36.

'Pulse S5 :is shown to be of a smaller width and maytherefore beregarded as representing a modulating signal of negative potential. Thedenection ofthe beam in response to this Apulse produces a coincidencewith the collector I2a for a duration corresponding to .the pulse width,the output .pulse lthereoi being represented at .42. Iikewise thegreater.widths o1' .pulses 31 and 38 AProduce =upon .delection oi the .beampulses .of

.60 greater amplitudeasindicatedat 43 and .44.

Graph iol. Fig. 4 shows va further principle of time modulation` whereinthe lpulsesare time displaced .relativeto theirnormal timing accordingto the instantaneous yalue .of the vmodulating .6 5 signal. l Thesepulsesareapplied.tothedeectng plates 3 and I0 .similarly as described.in.connec tiqnwith the .pulsetrain .34 .of Eig. 3. .Graph y' represents.the deflection of the beam during its trace 33 with respect to thecollector l2, .thus

.10 indicating the degrees oi coincidence of the de ilected lportionstherewith. Pulse 461s shown to be -in an unmodulated .position and-according .no .graph j producesa.50% coincidence between the .beam and,the ,collector `I2b, as indicated at .25 .46a, ,.thereby.fproducinc.anaverage now of cur- .5 rent las .indicated rat A1. The 'pulse-48,fhowever. is .shown to beinahe extreme-position-offmodu- ,lation and insuchposition; the deflection at '48a is shown .to be displaced to oneside of :the fcollector I2d. Thus, the rcircuit yIB doesfnoteonductcurrentfor the pulses'in thisextremeposition. Pulsesl and Ellwarevshownto bedis placed a given distance inppposite directions from 'theCentered -position` ofpulse l.46, and they produce. according.totheresulting degree of coincidence -of the beam vand collector I2output pulses 5I .and 52,A respectively.

In Fig. 5 .a-collector arrangement :is shown wherein the screen I Iincludes a liuoresoent coating'53. The outer main .portion of -thescreenis coated .with an opaque substance zasindicated at 54, vleaving asmallopening .at'55 over-which-a selenium. type .of photocell 551spositioned. .Atype of a cell other than selenium may.of course-be lused.This selenium cell isresponsive to the light .produced by the .beam onthe-uorescentfsub- .stance 53 so thatfw-hen the beam-is keyedon ordeflected for coincidence with the fluorescent screen area of aperture55, .the cell responds to produce aliiow of current in outputcircuit-Ail, the

amplitudeof .which corresponds to the'degree of coincidence of the beamwith respect to the aperture area. When the selenium cell is used it-maybe desirable toadd .ampliers to circuit I6 to boost the amplitude -ofthe outputpulses.

In Eig. 6V a variation of the plrotoelectric cell is shown utilizingthe. ordinary gas or Iphotocell las indicated at 58. Disposed in spacedrelation .in front of-the-.ucrescent coated screen I'I is abarrier'plate 59 .havingan aperture 60 in alignment with the cell 58 anda lens 6I, whereby an area 62 of the fluorescent screen is lfocused uponthe cell 58. The. cell 53 thus-responds-to thecoincidence .of the beamwith the area GZto producepulse energy as hereinbefore described inconnection with Figs. 2, -3 and 4.

In'Flg. 'I a cathode rayitube163 is shown similar in construction to thetube .31ct Fig. 1, exceptthat the collector arrangement is of thesecondary emission type. rI'Ihe collector, or rather, beam sensitiveequipment of this tube, includes a dynode 64 which is located in spacedrelation to a barrier plate 65. The barrier plate has an aperture 66 inalignment with the dynode $4 whereby the beam when in coincidence withthe aperture 66 impinges upon the dynode 64, thereby causing secondaryemission of electrodes from dynode 6d to the barrier plate G5. In orderto provide this condition the barrier plate 65 is maintained at a highpotential HB while the dynode 64 is maintained at a lower potential LBas indicated by connection 61, movable contact 68 and bias source 69. Inthe positions shown in Fig. 'I for contact 2U, 68, l0 and 1I, the pulseenergy from receiver I is applied together with cut-off bias HC fromsource 'I2 to the grid 5 the positive side oi' said source beingconnected to the cathode via ground. The bias HC maintains the grid atcut-ofifso that only the pulse energy applied thereto keys the 'beam onand ol similarly as hereinbefore described in connection with Fig. 1.The operation of the tube 63 is substantially the same as described inconnection with tube 3 of Fig'. 1 except that the secondary emissionfeature of this tube provides a much greater signal amplitude outputthan is obtainable, for example, by collector I'2 of Fig. l or theselenium cell of Fig. 5. The dynode arrangement has a further advantagein that a fluorescent screen is not used thereby avoiding halatlondefects that occur O I O ,casacca infthe fluorescent coating and .glassof screen I- I,

and in addition allows the return current;to.:.ow through theVdynode-anode circuit rather than through thebeaxn1 therebyravoiding:spaceecharge eifectsras-well:asthejhighrimpedance-effectof the beam.

-.Besides, the-keyed on-and oicontrol: ofzthegrid 5,-1the deflection of:thevbeam may be --controlled by the pulses over connection .2itoplatesaB, I0 byswitchingcontactslli and 23- to` therightsimilarlyfasfdescribedin 'connection with the circuit of;Fig. l.ifilhen-.thisrhangeis made it lwillralso Abe desirable-to shiftthescontacts y'It and 1I to .the left so asto provide a cut-oft biasfrom source .13 :to A grid f5. In ltbis condition f the Voperation issubstantially :the samei ashereinbefore described in connectionwithFigs. 3 and4, .with theexception :that the. output Acurrent is .here.produced by secondary emissionfbetween elements .6'4 and 65.

AInaddition to theseitwo beam control operations, the coactiverelationship betweenthe beam andthe dynode maybe oontrolleciby varyingthe sensitivity-of .the dynode in accordance withthe pulse energy. 'Thisisaccomplished 'oy placing in Fig. 7 all of thecontacts 20, 23, B8, Toand-1I to the left. In tlnscondition, the pulses ffrom receiver I areapplied through contacts 26 and lil and over connection-51 to the dynode54. 'In addition, the dyncde 64 is provided with aout-off bias fromsource i4 thrcugh-contact'li-.- Thus,

lthe dynode in the absenceof -pulses will not respond to theelectron-beam, but'when'biased accoi-ding to the energy ci' the timemodulated pulses will respond according to the degree of coactivecoincidence of the beam therewith, thereby l producing a. correspondingpulse ainplitude output. (In this case it may be necessary to reversethepolarity of the pulses from. the preceding in ordertotcause thedynodepotential to drop.v during the. arrival ofv .eacl1.pu.lse.)

WhileA we have .disclosed the principles ofcur invention in'connectionwith specic apparatus, it will be clearly understood that such apparatusis given by way of illustration only and not in restriction of the scopeof the invention as set forth in the objects and the appended claims.

We claim:

l. A demodulator for time modulated pulses comprising means -orproducing a beam of energy, means for causing said beam to sweep througha cyclic movement in synchronism with the timing of said pulses in theabsence of modulation, whereby coincidence of said pulses and a givenpart of said beam movement is varied in proportion to the amount of timemodulation of said pulses, and means for causing a iiow of electricalenergy proportional in amplitude to the degree of coincidence of saidpulses and said given part of the cyclic movement of said beam.

2. A demodulator according to claim 1, wherein the means for causingflow of energy includes means for keying the beam on and off accordingto the leading and trailing edges of each pulse.

3. A demodulator according to claim 1, wherein the means for causing nowof energy includes means for deflecting the beam from its normalmovement with respect to said given part of its cyclic movementaccording to the energy of said pulses.

4. A demodulator according to claim l, wherein the means for causingiiow oi' energy includes means responsive to. energy of said beam andmeans for controlling ,the responsiveness 0f said 7 responsive meansaccording to the energy of said pulses.

5. A demodulator according to claim 1, wherein the means for causing thebeam to have a cyclic sweep movement includes means for producing avoltage in response to the time modulated pulses which is ofsubstantially constant cyclic pattern, and means for deflecting saidbeam according to said voltage. 1

6. A demodulator for time modulated pulses comprisng means for producinga beam of energy, a beam sensitive device, means for causing said beamto sweep through a cyclic movement, the path of which bears a givenrelationship with respect to the location of said device, means forcausing said beam to coincide with said device in response to at leastcertain of said pulses, and a circuit associated with said device forconducting a iiow of current in response to coincidence of said beam andsaid device. l

'1. A demodulator according to claim 6, wherein said beamis anelectronic beam, and said device includes an electron responsiveelement.

8. A demodulator according to claim 6, wherein said device includesmeans for producing light upon coincidence with said -beam and meansre-l sponsive to intensity of said light to produce ilow of current.

9. A demodulator according to claim 6, wherein said device includes .anuorescent screen responsive to said beam for producing light. a lightresponsive cell associated with said screen and means for defining theactive area of said screen with respect to said cell.

10. A demodulator a'ccording to claim 6, .wherein said device includes abarrier disposed in the path of said beam, said barrier having anaperture therein, a dynode disposed in alignment with said aperture forinterception of said beam when said beam is projected through saidaperture.

11. A demodulator for time modulated pulses comprising means forproducing a cathode ray beam, means for producing a sweep voltage forcontrolling the cyclic movement of said beam to pulses.

cause said beam to follow a given path, means for synchronizing saidsweep voltage with the timing of said pulses in the absence o!modulation, a beam responsive device for producing a current when saidbeam coincides with said device, and means to cause said beam tocoincide with said device in accordance with the time characteristics ofat least certain of said pulses.

12. A demodulator according to claim 11, wherein said device includes abarrier member having an aperture for passage of said beam, and a dynodeelement disposed in alignment with said aperture for interception of thebeam passing therethrough.

13. A demodulator according to claim 11, wherein the means forcontrolling said beam in accordance with said pulses includes means forkeying the beam on and on according to the leading and trailing edges ofeach pulse.

14. A demodulator according to claim 11, wherein the means forcontrolling said beam in accordance with said pulses includes means fordeecting the beam from its normal path of movement in response to theenergy of said pulses,

mE LABIN.' DONALD D. GRIEG.

REFERENCES CITED The followingv references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,344,745 Somers Mar. 21, 1944

